Cells can be taken from tissues and grown or proliferated extracorporally. Under these conditions, some cell types develop properties which allow unlimited propagation, through permanently repeated mitoses. These cells are denoted as so-called permanent cell lines. Freshly removed cells from tissues (e.g., surgical samples, or tissues from experimental animals) most often do not display these properties. Cells of such so-called primary cultures either lack mitotic activity or perform only a few mitoses, i.e., these cells can only be cultured for a short period of time and only under loss of most of their original functional characteristics (dedifferentiation).
Adhesion of cells to their growth support and the appropriate differentiation of cells is largely dependent on the properties of the growth support (growth substrate).
The introduction of microporous growth supports made up of thin foils of either organic or inorganic materials led to an improvement in differentiation of cells in culture. This is specifically the case for those cells growing as monocellular layers (monolayers) like epithelial and endothelial cells. The culture containers used for that purpose in most cases are hollow cylinders which are sealed on one side by microporous foils on which cells are growing. These cylinders are then placed into larger culture containers in a way that culture medium can reach the cell monolayers from both the apical and the basolateral side (U.S. Pat. No. 4,608,342),the teachings of which are incorporated herein by reference. The culture medium is replaced at certain intervals. Cultures of this type are denoted as "static". Under these conditions, compounds produced by cells can accumulate in the culture medium and exert negative effects on cell growth and differentiation. For this reason, improved conditions have been developed. Microporous growth substrates can, for example, be placed between two concentric circular mounting unites (cell carrier) and then cells seeded and attached to the growth support. Such cell carriers can then be transferred to a culture medium chamber which is separated by the carrier in two halves. Each half of the chamber can then be perfused with the same medium or media differing in composition. The cell carriers can also be stapled in a specific culture chamber and per(i)fused with culture medium (DE-PS 3923 279), the teachings of which are incorporated herein by reference. These cell culture systems are easy to handle and offer the possibility to grow and/or maintain primary cultures over longer periods of time than under static culture conditions either using solid (plastic, glass) or microporous supports. However, they have the disadvantage that only culture containers for cell carriers having a very small growth area, i.e., about 0.9 cm.sup.2, are obtainable. The per(i)fusion cell apparatus in which cell carriers can be stacked in order to obtain enough material for biochemical/cell biological analyses has the disadvantage of insufficient oxygenation of the medium between the cell carriers. Furthermore, both devices display mixing inhomogenities during continuous replacement of the growth medium by per(i)fusion.